The present invention relates to improvements in decelerators, and more particularly to an improved structure to be attached to a munition deployed from an aircraft capable of stably decelerating the descent of the munition as it drops toward the earth.
As munitions of varying sizes are deployed from aircraft, it is necessary in order to control the effective descent to reach a selected target to slow their release speed and to slow their descent. Further, a speed retarder must have the capability of slowing the speed of release and descent in a stable manner so that the trajectory and location of landing relative to a target can be calculated and determined. The release of a munition from an aircraft at high speeds will subject a deceleration device to a severe shock at the beginning of deceleration and until the speed of descent reaches a satisfactory velocity. In addition to slowing the munition from its high speed, such decelerator must continue to be effective in the stabilization mode for the remainder of the descent of the munition.
Various devices have been employed which have not been satisfactory in that many of these will fail due to the severe shock occurring with sudden retardation of speed which occurs as the munition is released from an aircraft at relatively high speed. The resultant shocks are often sufficient to cause structural failure and damage to the retarding device as well as to the munition itself. Prior art devices which are capable of retarding speed often utilized parachutes, finned stabilization and Ballute technology, but a common difficulty occurring is that the excess of speed at the time of release of the munition often over stresses the decelerator and causes it to fail. Devices based on the parachute principle will provide drag for deceleration, but upon sudden opening at high speed, will often rupture and become disoriented or break. Such devices as well as other devices which additionally stabilize the descent of the munition often fail at higher speeds and if effective at higher speeds, become ineffective and unstable at slower speeds thereby generating unstable trajectories and unstable descent patterns wherein the munition tumbles instead of descending properly.
There is a wide separation in the velocity which must be obtained for the munition in its final descent and the speed in which it is initially deployed from the airplane. Other problems which are encountered are that the decelerator may have to insure that the explosive weapon impacts the surface more nearly vertical than horizontal, and therefore a decelerator which is capable of performing this function must be reliable and predictable. It is also important that such a decelerator be relatively reasonably priced for quantity production.
In a typical mission, weapons or munitions will be deployed at sonic or supersonic speeds. At such speeds, earlier forms of decelerators such as the parachutes or metal vanes, are prone to failure and have proven not to be acceptable. In the development of decelerators, the concept of a closed inflatable decelerator was pioneered by Goodyear Aerospace Corporation as a Ballute. This balloon-like device is capable of being packed in a compartment in the rear of the munition such as a 500 pound bomb. Upon release from the aircraft, the Ballute is released and the air is scooped into the device through inlets in its side. The size of the inflation is determined by the drag force which is required for the particular application. Simple rounded shapes tend to be unstable in an airflow, so inflatable decelerator designs must include a turbulence generator, often referred to as a "burble fence". Decelerators of this large type have been in production over the years and serve certain circumstances, but are not satisfactory for all applications.
Another form of decelerator which has been developed is a smaller version which is used to slow small bomblets which are typically released in large quantity from unitized containers. Because the needed quantities range into the millions, the decelerators must be very simple and inexpensive. One form of decelerator which has been developed for the foregoing purposes is disclosed in U.S. Pat. No. 4,565,341. This structure incorporates a pseudo-conical forward surface and an essentially flat rearward surface. The requirements of this structure make it difficult to manufacture and too expensive for many applications, and the structure of the present invention has been discovered to provide advantages in manufacture and performance over a structure such as that disclosed in the aforesaid patent.